More detailed information about left posterior fascicular block

• the normal left ventricular activation proceeds first down the left bundle branch, and then simultaneously through its two fascicles (left anterior fascicle and left posterior fascicle)
• left posterior fascicular block (LPFB), also known as left posterior hemiblock, is much less common than left anterior fascicular block (LAFB) - this is due to a number of factors:
  • the posterior fascicle is a thicker structure than the anterior fascicle
  • posterior fascile has a dual blood supply
  • the anatomic location of the posterior fascicle is away from more turbulent ventricular blood flow
• ECG changes in LPFB:
  • QRS interval <0.12 seconds
  • right axis deviation
  • rS pattern in the lateral limb leads (I and aVl)
  • qR complex in the inferior leads (II, III, and aVf)
  • no evidence of right ventricular hypertrophy
• LPFB is a rare finding
  • LPFB is nonspecific for cardiac disease - however coronary artery disease is the most common cause
  • other associations for LPFB include hypertensive heart disease, aortic valvular pathology, and fibrocalcific disease of the cardiac skeleton
  • LPFB is the least common intraventricular conduction block seen in acute myocardial infarction
• data on established LPFB are insufficient assess prognostic significance

Reference:

1. Harrigan RA et al. Electrocardiographic manifestations: bundle branch blocks and fascicular blocks. The Journal of Emergency Medicine 2003;25(1):67–77
2. Rowlands DJ.Left and right bundle branch block, left anterior and left posterior hemiblock. Eur Heart J. 1984 Mar;5 Suppl A:99-105.